Flexible tubes for fixed peripheral venous cannulas

ABSTRACT

The invention concerns flexible tubes for delivering solutions for perfusion or injection into the peripheral vascular system. The invention is characterized in that said flexible tubes are manufactured by coextrusion process from a composite polyamide and polyurethane laminate, the inner layer facing the lumen and the outer layer being respectively formed with polyamide and polyurethane. The desired properties of said flexible tubes, such as buckling stability, flexural rigidity or free flow capacity, can be adjusted and customized on the basis of the wall thickness distribution which, preferably has a PA/PUR ratio of 50:50 to 70:30, and on the basis of the Shore hardness of the initial constituents.

Flexible tubes for fixed peripheral venous cannulas are used in theperipheral vascular system to deliver solutions for infusions andinjections as well as for taking blood. Solutions or injections aredelivered or blood taken from a vein in the peripheral vascular system,meaning far from the heart, by means of a flexible tube or plasticcannula. The materials used for this according to prior art are FEP orPUR in the form of single-material flexible tubes, with or withoutradiopaque strips.

Several important properties of flexible tubes of FEP or PUR for fixedvenous cannulas are evaluated in the following Table 1. TABLE 1 Ten- Ri-Advanc- dency to Blood Mate- gid- Buckling ing inflam- compati- Roll-uprial ity resistance ability mation bility behavior FEP ++ − ++ −− − ++PUR + + + ++ ++ −

Explanattions

-   -   Rigidity=Resistance against bending as a result of radial        forces;    -   Buckling resistance=Resistance of the flexible tube to buckle        following deflection/bending around a narrow radius, so as to        prevent lumen closure and/or irreversible damage to the flexible        tube;    -   Advancing ability=Easy placement and positioning of catheter in        vessels due to axial stress without resistance worth mentioning;    -   Roll-up behavior=Contracting and compressing tendency of the        tube-shaped cannula (harmonica effect) caused by penetration of        skin, tissue and the vein as a result of application and gliding        resistance.

As shown in the above Table, FEP primarily distinguishes itself throughan extremely good advancing ability. However, it has the disadvantage ofbeing subject to higher incidences of buckling, which lead tointerference with or even a complete stop of the throughput, as well asthe strongly increased risk of injury and/or inflammation of thevascular walls.

In contrast, PUR has an acceptable buckling resistance and good bloodcompatibility and the risk of inflammation or injury to the vessel wallsis nearly zero.

The reason for the latter is that PUR becomes soft within a few minutesat body temperature, meaning that hardly any mechanical irritation ofthe vascular walls occurs.

However, PUR has the particular disadvantage of a noticeably higher“roll-up” risk for the cannula during the application.

It is therefore the object of the present invention to make availableflexible tubes for fixed peripheral venous cannulas which combine thepositive properties of FEP with those of the PUR without also takingover the respectively negative properties (see Table 1 for this).

Surprisingly, this object was solved with a flexible tube design forfixed peripheral venous cannulas, which uses a composite laminate,comprising an inside layer of polyamide and an outside layer ofpolyurethane.

The considerations that went into solving this problem are described inthe following:

-   -   Homo polymers are used for producing tube-shaped extruded        products, wherein co-polymers or polymer mixtures are primarily        used, especially in the field of medicine.

However, if the spectrum of properties for standard materials orself-formulated materials is not sufficient, composite laminates ofmaterials having different properties are used. To be considered arecases where the inside surface of the flexible tube must have noticeablydifferent properties than the outside surface, for example if theoutside surface must have a good bonding ability and the inside surfacea high chemical resistance.

The macroscopic properties of such conventional composite laminates,e.g. rigidity or bending resistance, are determined by the sum of theindividual material property shares, for example as described in thefollowing U.S. Pat. No. 4,385,632. Described in this reference is acomposite laminate for an angiography catheter, provided with a soft,a-traumatic tip made exclusively from polyurethane, a transition regionand a main flexible tube section consisting of an internal polyamidelayer and an external layer of polyurethane with an approximate wallthickness ratio of 50:50.

It is the object of this embodiment in the form of a composite laminateis to meet the following requirements:

-   -   To have a soft, a-traumatic non-reinforced polyurethane tip;    -   To attach this tip firmly to the flexible catheter tube;    -   To ensure a correspondingly high rigidity of the catheter with        low wall thickness, which is necessary since the radiopaque        medium is applied with high pressure (up to 1200 psi) and a        bursting of the catheter during this operation must be safely        avoided.

The present invention, on the other hand, is designed to achieve theabove-described flexible tube properties for tubes used as fixed venouscannulas, wherein these properties must clearly exceed the sum of theindividual material properties. Such combinations of material propertiesshould be achievable only if the systems exhibit a certain synergiceffect and the materials used are furthermore precisely adapted to therespective application case.

According to one important requirement, the flexible tube should be asrigid as possible during the insertion into the body and as flexible aspossible while remaining in the body. These properties, which initiallyseem to be mutually exclusive, can surprisingly be achieved with thematerial combination according to our invention. This is due to the factthat PUR with a shore hardness of 60 D, for example, softens to 50 D at37° C. within 5 minutes. In contrast, the flexibility of PA is primarilyinfluenced by the absorption of moisture, wherein this action isinsignificant as compared to PUR and requires a longer period of time.

These in part opposing and in part super-imposed effects not only makepossible—depending on the relative wall thickness of PUR to PA and therespective shore hardness of the individual materials—to preciselyadjust on the one hand the required rigidity for placing the flexibletube and, on the other hand, the required flexibility necessary forremaining inside the body. Rather, it was particularly surprising thatother properties necessary for using the flexible tube could also beadjusted purposely, namely the rigidity, the buckling resistance, theadvancing ability, and the roll-up behavior.

With this invention, the user therefore has many options to purposelyand easily influence the flexible tube properties of fixed venouscannulas, meaning so-to-speak adjust them precisely to the requirements.That is not possible with the currently used single-material flexibletubes according to prior art.

The desired properties of flexible tubes for fixed peripheral venouscannulas furthermore can in most cases be guaranteed even withfluctuations in the raw-material quality by varying the respective layerthicknesses of the co-extruded flexible tube.

The sum of all properties of the composite-material flexible tube canfurthermore be changed considerably, but in a simple manner, withoutrequiring special formula mixtures by using different, commonly usedstandard raw materials with different mechanical properties.

However, such formula mixtures can additionally be used and can resultin a further optimization and/or a precise adjustment of the flexibletube properties.

The following Table 2 provides a summary of the properties of thecomposite laminate according to the invention, comprising an external PAlayer and an internal PUR layer for the flexible tube, as compared totubes made from the starting substances PA and PUR and/or FEP: TABLE 2Buck- Ten- Ri ling Advanc- dency to Blood Mate- gid- resis- ing inflam-compati Roll-up rial ity tance ability mation bility behavior FEP ++ −++ −− − ++ PUR + + + ++ ++ − PA ++ + ++ + + ++ PA/PUR ++ ++ ++ ++ ++ +++ = good++ = very good− = poor−− = very poor

The following is intended to explain with the aid of an exemplaryembodiment whether the invention is suitable for use as flexible tubefor a fixed peripheral venous cannula. The tested flexible tube, used asfixed peripheral venous cannula, has an external diameter of 1.07 mm, aninternal diameter of 0.79 mm and is provided with radiopaque strips.

If this flexible tube with PA internal layer and PUTR external layer isdeflected by 180° around a pin with 4 mm diameter, it does not buckle inthe temperature range between 23° C. and 37° C.

For a comparison:

-   -   A FEP flexible tube will definitely buckle at this temperature        range and will be damaged in the process, such that the        throughput, for example of infusion solution, is reduced or even        blocked permanently. Owing to this irreversible damage, it        becomes necessary to replace the flexible tube for the fixed        venous cannula, which leads to unnecessary stress for the        patient, particularly if the patient has hard to puncture veins.    -   A PUR flexible tube does not buckle at 37° C., to be sure, but        the danger of buckling at temperatures below 30° C. is rather        high—depending on the wall thickness and external diameter—so        that the pure PUR flexible tube has only a limited usability for        fixed peripheral venous cannulas.

1. Flexible tubes made from polymers for use as fixed venous cannulas,said flexible tubes comprising a composite laminate of polyamide andpolyurethane, wherein the inside layer facing the lumen is a polyamidelayer and the outside layer is a polyurethane layer.
 2. The flexibletubes as defined in claim 1, characterized in that the polyamide isselected from the group polyamide 11, polyamide 12 orpolyetherblockamide.
 3. The flexible tubes as defined in claim 1,characterized in that the polyurethane is selected from the grouppolyetherpolyurethane or polyesterpolyurethane.
 4. The flexible tubesused for fixed peripheral venous cannulas as defined according to claim1, characterized in that the composite laminate preferably is acoextruded material.
 5. The flexible tubes used for fixed peripheralvenous cannulas as defined according to claim 1, characterized in thatthe composite laminate has a layer thickness ratio of PA internal layerto PUR external layer ranging from 20:80 to 80:20 and preferably from50:50 to 70:30.
 6. The flexible tubes used for fixed peripheral venouscannulas as defined according to claim 1, characterized in that theinternal and/or external layer is provided with one or severalroadipaque strips.